The present invention relates to a semiconductor device fabrication method, more specifically a method for fabricating a semiconductor device including insulation film of low dielectric constant.
Recently, as semiconductor devices are increasingly integrated, the interconnection width and the interconnection pitch are set increasing much smaller. It is proposed to make the interconnection pitch 0.1 μm or below. The parasitic capacitance between the interconnections is inversely proportional the interconnection pitch, and the parasitic capacitance between the interconnections is increased as the interconnection pitch is made smaller. The increase of the parasitic capacitance between the interconnections leads to the delay of the propagation speed, which is a factor for blocking the improvement of the operation speed of the semiconductor devices. To decrease the parasitic capacitance between the interconnections it is effective to use materials of low dielectric constants as the materials of the inter-layer insulation films.
Conventionally, as materials of the inter-layer insulation film, inorganic films, as of silicon dioxide (SiO2), silicon nitride (SiN), Phosphorus-Silicate Glass (PSG), etc., have been used. As materials of the inter-layer insulation film, organic film, etc., as of polyimide, etc., have been used. For example, the dielectric constant of SiO2 film formed by CVD is about 4.
As an insulation film having a dielectric constant lower than SiO2 film, SiOF film is proposed. The dielectric constant of SiOF film is about 3.3-3.5. However, to sufficiently lower the parasitic capacitance between the interconnection, it is necessary to use insulation films of further lower dielectric constants.
Recently as insulation films of very low dielectric constants, porous insulation film is noted. The porous insulation film is a film having a number of pores therein. A porous insulation film is used as a material of the inter-layer insulation films, whereby the parasitic capacitance between the interconnection can be decreased.
Following references disclose the background art of the present invention.
[Patent Reference 1]
Specification of Japanese Patent Application Unexamined Publication No. 2002-26121
[Patent Reference 2]
Specification of Japanese Patent Application Unexamined Publication No. 2003-68850
However, it cannot be said that the porous insulation film, in which a number of pores are formed, is mechanically sufficiently strong. Cracks are often made in the insulation film, and the insulation film is often broken in bonding.